This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The segmented, single-stranded RNA genome of the Influenza A Virus is packed by a nucleoprotein and a polymerase into Ribonucleoprotein complexes (RNPs), forming an antiparallel helix. The RNA is encapsidated by multiple nucleoproteins (~56kDa) and a trimeric polymerase is associated to the complex Despite the fundamental importance of RNPs for both viral replication, as well as the formation of infectious virion, its native structure remains unknown. The inherent flexibility of these complexes poses significant difficulties for three-dimensional structure determination.